In 3GPP (3rd Generation Partnership Project), standardization of LTE-Advanced (LTE (Long Term Evolution)-A) has been fostered as the 4th generation mobile communication system to realize further higher-speed and larger-capacity communications than LTE which is development standard in the 3rd generation mobile communication system. LTE-A has important issues to improve throughputs of cell-edge users as well as to realize higher-speed and larger-capacity communications, and as a way of this, study has been made of a relay transmission technique for relaying radio communications between a radio base station apparatus and a mobile terminal apparatus. With use of this relay transmission technique, it is expected to extend the coverage effectively in such a place that wired backhaul link is difficult to establish.
In the relay technique, there are type I relay (L3 relay) and type II relay (Advanced-L1 relay, Advanced-L2 relay). Type I relay is such a relay technique that a cell of a radio relay station apparatus (relay node: RN) has its own cell ID and the radio relay station apparatus transmits common/shared control signals for the own cell. Accordingly, the relay node acts as a radio base station apparatus for a mobile terminal apparatus (user terminal: UE). And, the relay node has a specific scheduler. Accordingly, type I relay makes a contribution to extension of a coverage via a radio backhaul link between the radio base station apparatus (Donor eNode B: DeNB) and the relay node RN. This type I relay has been standardized in LTE Release-10 (see Non Patent Literatures 1, 2).
On the other hand, type II relay is such a relay technique that a cell of the relay node does not have its own cell ID and the relay node does not transmit cell-specific reference signals or control signals. In type II relay, DeNB allocates its own resources and allocates resources of the relay node (scheduling). Accordingly, type II relay makes a contribution to improvement of user throughput thereby to increase the capacity. This type II relay is expected to be standardized in Release-11 LTE or later. Note that L1 relay is a relay technique called booster or repeater, which is an AF (Amplifier and Forward) type relay technique in which downlink reception RF signals from a radio base station apparatus DeNB are power-amplified and transmitted to a mobile terminal UE. And, L2 relay is a DF (Decode and Forward) type relay technique in which downlink reception RF signals from the radio base station apparatus DeNB are demodulated and decoded, then, coded and modulated again and transmitted to the mobile terminal UE.